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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Ada 2012 Constraints (WRT an Ada IR)
Date: Tue, 29 Nov 2016 17:52:18 -0600
Organization: JSA Research & Innovation
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Xref: news.eternal-september.org comp.lang.ada:32525
Date: 2016-11-29T17:52:18-06:00
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"Shark8" <onewingedshark@gmail.com> wrote in message 
news:c06ee4e6-d616-4e01-ba2e-cb111a81f6f6@googlegroups.com...
>So, with Ada 2012 we gained some really nice possibilities with the way to 
>express constraints, the
>downside is that there's now a fairly wide range of ways to express 
>constraints on types. Obviously
>these differences must be accounted for, but the are functionally 
>equivalent, for example:
>
>Subtype P0 is Natural range Natural'Succ(Natural'First)..Natural'Last;
>Subtype P1 is Integer range 1..Integer'Last;
>Subtype P2 is Integer with Static_Predicate => P2 in 1..Integer'Last or 
>else raise Constraint_Error;
>Subtype P3 is Integer with
>  Static_Predicate  => P3 in 1..Integer'Last,
>  Predicate_Failure => raise Constraint_Error;
>
>Now, these should be generally the same way of writing the same thing (ie 
>"Positive") -- though
> I'm not completely certain that this is the case in terms of subtle 
> semantics (am I missing something?)

P2 is different than the others when used in a membership:

    Obj in P2

would raise Constraint_Error rather than return False (like the others) if 
Obj has the value 0. It's not recommended.

P0 and P1 are more likely to be optimized by a compiler (just because of the 
many years of history). Perhaps P3 will catch up, but I wouldn't hold my 
breath on that.

                               Randy.